The Hour of Twilight is the fulfillment of a long chain of events that were planned by the Old Gods.

A very ancient prophecy speaks of the Hour of Twilight, the final days of the world and if the Old Gods that were chained long ago had their way set in motion, this chain of events would enact their final vision to remake the world in their image.

It possibly started with the reopening of Ahn'Qiraj where C'Thun rose beneath the lands of Silithus.

There is a chain of events in motion where the Old Gods are rising, their ancient machinations are finally paying off, and Deathwing ultimately is their greatest hammer. While he has his own machinations, trying to settle his own domination over Azeroth, he was corrupted by the Old Gods from the start and in this final hour, he is pretty much the greatest weapon for the Old Gods to unleash.[1]

After the Hour of Twilight, every lifeform on Azeroth will be dead and rotting, except twilight dragons. In Ysera's vision of the Hour of Twilight, all five Aspects, including Deathwing, lay dead at Wyrmrest Temple, killed by their own powers.[2]

Deathwing yells: The sun has set on this mortal world, fools. Make peace with your end, for the Hour of Twilight falls![3][4]

Fandral Staghelm says: Not so fast, son of Durotan. You and your allies have certainly set us back. But, the Hour of Twilight cannot be averted! The Twilight Prophet knows that you, and you alone, are our final obstacle. He sent me to remove you from the game.[5]

Ragnaros yells: THE END COMES, SON OF DUROTAN...THE FINAL HOUR OF TWILIGHT.[citation needed]